From: Paul Mackerras <paulus@ozlabs.org>
To: "Cédric Le Goater" <clg@kaod.org>
Cc: kvm@vger.kernel.org, kvm-ppc@vger.kernel.org,
linuxppc-dev@lists.ozlabs.org,
David Gibson <david@gibson.dropbear.id.au>
Subject: Re: [PATCH 19/19] KVM: introduce a KVM_DELETE_DEVICE ioctl
Date: Tue, 22 Jan 2019 16:42:53 +1100 [thread overview]
Message-ID: <20190122054253.GH15124@blackberry> (raw)
In-Reply-To: <20190107191006.10648-3-clg@kaod.org>
On Mon, Jan 07, 2019 at 08:10:06PM +0100, Cédric Le Goater wrote:
> This will be used to destroy the KVM XICS or XIVE device when the
> sPAPR machine is reseted. When the VM boots, the CAS negotiation
> process will determine which interrupt mode to use and the appropriate
> KVM device will then be created.
What would be the consequence if we didn't destroy the device?
The reason I ask is that we will have to be much more careful about
memory allocation lifetimes with this patch. Having KVM devices last
until the KVM instance is destroyed means that we generally avoid
use-after-free bugs. With this patch we will have to do a careful
analysis of the lifetime of the xive structures vs. possible accesses
on other threads to prove there are no use-after-free bugs.
For example, it is not sufficient to set any pointers in struct kvm or
struct kvm_vcpu that point into xive structures to NULL before freeing
the structures. There could be code on another CPU that has read the
pointer value before you set it to NULL and then goes and accesses it
after you have freed it. You need to prove that can't happen,
possibly using some sort of explicit synchronization that ensures that
no other CPU could still be accessing the structure at the time when
you free it. RCU can help with this, but in general means you need
RCU synchronization primitives (rcu_read_lock() etc.) at all the
places where you use the pointer, which I don't think you currently
have.
If there is a good fundamental reason why this can't happen, even
though you don't have explicit synchronization, then at a minimum you
need to explain that in the patch description, and ideally also in
code comments.
Paul.
next prev parent reply other threads:[~2019-01-22 5:51 UTC|newest]
Thread overview: 135+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-07 18:43 [PATCH 00/19] KVM: PPC: Book3S HV: add XIVE native exploitation mode Cédric Le Goater
2019-01-07 18:43 ` [PATCH 01/19] powerpc/xive: export flags for the XIVE native exploitation mode hcalls Cédric Le Goater
2019-01-09 3:33 ` David Gibson
2019-01-09 13:08 ` Michael Ellerman
2019-01-09 13:38 ` Cédric Le Goater
2019-01-07 18:43 ` [PATCH 02/19] powerpc/xive: add OPAL extensions for the XIVE native exploitation support Cédric Le Goater
2019-01-09 4:26 ` David Gibson
2019-01-07 18:43 ` [PATCH 03/19] KVM: PPC: Book3S HV: check the IRQ controller type Cédric Le Goater
2019-01-09 4:27 ` David Gibson
2019-01-22 4:56 ` Paul Mackerras
2019-01-23 16:24 ` Cédric Le Goater
2019-02-04 0:50 ` David Gibson
2019-02-04 10:16 ` Cédric Le Goater
2019-01-07 18:43 ` [PATCH 04/19] KVM: PPC: Book3S HV: export services for the XIVE native exploitation device Cédric Le Goater
2019-01-11 4:09 ` David Gibson
2019-01-07 18:43 ` [PATCH 05/19] KVM: PPC: Book3S HV: add a new KVM device for the XIVE native exploitation mode Cédric Le Goater
2019-01-22 5:05 ` Paul Mackerras
2019-01-23 16:28 ` Cédric Le Goater
2019-01-28 17:35 ` Cédric Le Goater
2019-01-30 4:29 ` Paul Mackerras
2019-01-30 7:01 ` Cédric Le Goater
2019-01-31 3:01 ` Paul Mackerras
2019-02-01 17:03 ` Cédric Le Goater
2019-02-04 4:25 ` David Gibson
2019-02-04 11:19 ` Cédric Le Goater
2019-02-05 5:26 ` David Gibson
2019-01-07 18:43 ` [PATCH 06/19] KVM: PPC: Book3S HV: add a GET_ESB_FD control to the XIVE native device Cédric Le Goater
2019-01-22 5:09 ` Paul Mackerras
2019-01-23 16:48 ` Cédric Le Goater
2019-02-04 4:45 ` David Gibson
2019-02-04 11:30 ` Cédric Le Goater
2019-02-05 5:28 ` David Gibson
2019-02-05 12:55 ` Cédric Le Goater
2019-02-06 1:23 ` David Gibson
2019-02-06 7:21 ` Cédric Le Goater
2019-02-07 2:49 ` David Gibson
2019-02-07 9:03 ` Cédric Le Goater
2019-02-08 5:15 ` David Gibson
2019-02-08 7:58 ` Cédric Le Goater
2019-02-08 21:53 ` Paul Mackerras
2019-02-09 9:41 ` Cédric Le Goater
2019-02-11 2:38 ` David Gibson
2019-02-11 6:42 ` Benjamin Herrenschmidt
2019-02-12 22:07 ` Cédric Le Goater
2019-01-07 18:43 ` [PATCH 07/19] KVM: PPC: Book3S HV: add a GET_TIMA_FD control to " Cédric Le Goater
2019-01-07 18:43 ` [PATCH 08/19] KVM: PPC: Book3S HV: add a VC_BASE control to the " Cédric Le Goater
2019-01-22 5:14 ` Paul Mackerras
2019-01-23 16:56 ` Cédric Le Goater
2019-02-04 4:49 ` David Gibson
2019-02-04 15:36 ` Cédric Le Goater
2019-01-07 18:43 ` [PATCH 09/19] KVM: PPC: Book3S HV: add a SET_SOURCE " Cédric Le Goater
2019-02-04 4:57 ` David Gibson
2019-02-04 19:07 ` Cédric Le Goater
2019-02-05 5:35 ` David Gibson
2019-02-05 13:39 ` Cédric Le Goater
2019-01-07 18:43 ` [PATCH 10/19] KVM: PPC: Book3S HV: add a EISN attribute to kvmppc_xive_irq_state Cédric Le Goater
2019-01-07 18:43 ` [PATCH 11/19] KVM: PPC: Book3S HV: add support for the XIVE native exploitation mode hcalls Cédric Le Goater
2019-01-22 5:23 ` Paul Mackerras
2019-01-23 6:44 ` Benjamin Herrenschmidt
2019-01-23 8:48 ` Cédric Le Goater
2019-01-23 10:26 ` Paul Mackerras
2019-01-23 10:48 ` Cédric Le Goater
2019-01-23 21:23 ` Benjamin Herrenschmidt
2019-01-07 18:43 ` [PATCH 12/19] KVM: PPC: Book3S HV: record guest queue page address Cédric Le Goater
2019-02-04 5:15 ` David Gibson
2019-02-04 15:37 ` Cédric Le Goater
2019-01-07 18:43 ` [PATCH 13/19] KVM: PPC: Book3S HV: add a SYNC control for the XIVE native migration Cédric Le Goater
2019-02-04 5:17 ` David Gibson
2019-02-04 15:39 ` Cédric Le Goater
2019-01-07 18:43 ` [PATCH 14/19] KVM: PPC: Book3S HV: add a control to make the XIVE EQ pages dirty Cédric Le Goater
2019-02-04 5:18 ` David Gibson
2019-02-04 15:46 ` Cédric Le Goater
2019-02-05 5:30 ` David Gibson
2019-01-07 18:43 ` [PATCH 15/19] KVM: PPC: Book3S HV: add get/set accessors for the source configuration Cédric Le Goater
2019-02-04 5:21 ` David Gibson
2019-02-04 16:07 ` Cédric Le Goater
2019-02-05 5:32 ` David Gibson
2019-02-05 13:03 ` Cédric Le Goater
2019-02-06 1:23 ` David Gibson
2019-02-06 1:24 ` David Gibson
2019-02-06 7:07 ` Cédric Le Goater
2019-02-07 2:48 ` David Gibson
2019-02-07 9:13 ` Cédric Le Goater
2019-02-08 5:15 ` David Gibson
2019-02-14 16:50 ` Cédric Le Goater
2019-01-07 18:43 ` [PATCH 16/19] KVM: PPC: Book3S HV: add get/set accessors for the EQ configuration Cédric Le Goater
2019-02-04 5:24 ` David Gibson
2019-02-05 17:45 ` Cédric Le Goater
2019-01-07 19:10 ` [PATCH 17/19] KVM: PPC: Book3S HV: add get/set accessors for the VP XIVE state Cédric Le Goater
2019-01-07 19:10 ` [PATCH 18/19] KVM: PPC: Book3S HV: add passthrough support Cédric Le Goater
2019-01-22 5:26 ` Paul Mackerras
2019-01-23 6:45 ` Benjamin Herrenschmidt
2019-01-23 10:30 ` Paul Mackerras
2019-01-23 11:07 ` Cédric Le Goater
2019-01-28 6:13 ` Paul Mackerras
2019-01-28 18:26 ` Cédric Le Goater
2019-01-29 2:45 ` Paul Mackerras
2019-01-29 13:47 ` Cédric Le Goater
2019-01-30 6:20 ` Paul Mackerras
2019-01-30 15:54 ` Cédric Le Goater
2019-01-31 2:48 ` Paul Mackerras
2019-01-29 4:12 ` Paul Mackerras
2019-01-29 17:44 ` Cédric Le Goater
2019-01-30 5:55 ` Paul Mackerras
2019-01-30 7:06 ` Cédric Le Goater
2019-01-23 21:25 ` Benjamin Herrenschmidt
2019-01-24 8:41 ` Cédric Le Goater
2019-01-28 4:43 ` Paul Mackerras
2019-01-29 13:46 ` Cédric Le Goater
2019-01-07 19:10 ` [PATCH 19/19] KVM: introduce a KVM_DELETE_DEVICE ioctl Cédric Le Goater
2019-01-22 5:42 ` Paul Mackerras [this message]
2019-01-23 18:39 ` Cédric Le Goater
2019-01-23 21:32 ` Benjamin Herrenschmidt
2019-02-04 5:26 ` [PATCH 17/19] KVM: PPC: Book3S HV: add get/set accessors for the VP XIVE state David Gibson
2019-02-04 18:57 ` Cédric Le Goater
2019-02-05 5:33 ` David Gibson
2019-02-05 11:58 ` Cédric Le Goater
2019-02-06 1:19 ` David Gibson
2019-01-22 4:46 ` [PATCH 00/19] KVM: PPC: Book3S HV: add XIVE native exploitation mode Paul Mackerras
2019-01-23 19:07 ` Cédric Le Goater
2019-01-23 21:35 ` Benjamin Herrenschmidt
2019-01-26 8:25 ` Cédric Le Goater
2019-02-04 5:36 ` David Gibson
2019-02-05 11:31 ` Cédric Le Goater
2019-02-05 22:13 ` Paul Mackerras
2019-02-06 1:18 ` David Gibson
2019-02-06 7:35 ` Cédric Le Goater
2019-02-07 2:51 ` David Gibson
2019-02-07 8:31 ` Cédric Le Goater
2019-02-08 5:07 ` David Gibson
2019-02-08 7:38 ` Cédric Le Goater
2019-01-28 5:51 ` Paul Mackerras
2019-01-29 13:51 ` Cédric Le Goater
2019-01-30 5:40 ` Paul Mackerras
2019-01-30 15:36 ` Cédric Le Goater
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